It's a special day at Namungalwe primary school in Ikanga district, Uganda. Instead of science or English, students are attending a mass drug administration (MDA) programme. Outside each classroom, a multicoloured height chart has been stuck on the wall and students queue for their turn to be measured. Teachers enter the students' height in a neat register and hand over the corresponding dose of Zithromax, an antibiotic used in the treatment and prevention of trachoma, an eye infection that can cause blindness.

There are hundreds more MDAs taking place in Uganda and around the world. Trachoma, which forces the eyelid to turn inwards and causes the eyelashes to scratch the cornea, is the leading cause of preventable blindness. More than 40 million people are infected with the disease; roughly half the global burden is concentrated in five countries (Ethiopia, Guinea, India, Nigeria and Sudan). The disease thrives among poor communities, where overcrowding, poor hygiene and lack of clean water help spread the bacteria.

It's estimated that trachoma costs $2.9bn a year in lost productivity. It also costs many children their education because they must care for blind relatives. In 1998, the World Health Assembly resolved to eliminate blinding trachoma by 2020. Twelve years on, progress is encouraging, thanks in part to the wide implementation of the WHO's Safe strategy: S stands for surgery (a simple operation to pull the eyelid back in the most advanced stage of the disease, called trichiasis); A for antibiotics; F for face-washing; E for environmental hygiene.

To date, the A component has been the most successful. In 1999, Pfizer, the pharmaceutical company producing Zithromax, decided to donate the drug for as long as it would take to eliminate the disease. "When we developed azithromycin [Zithromax], no one had trachoma in mind," explains Dr Jack Watters, Pfizer's vice president for external medical affairs. "So when we realised how effective it was at treating the infection, we decided to include it in the Safe strategy: there is little point in developing medicine unless all the people who need it can access it."

That still leaves surgery, face-washing and environmental hygiene. Sight Savers, an international NGO working to eliminate preventable blindness, estimates that there is a backlog of 9m trichiasis surgeries globally (5 million in Africa), which means that people are still at risk of going blind. In Ghana and Vietnam for instance, MDAs have stopped since prevalence has dropped below WHO levels, but both countries must work through their trichiasis backlogs to achieve elimination.

Simon Bush, director of African alliances and advocacy at Sight Savers, says the greatest challenge in the Safe strategy is promoting better facial and environmental hygiene: "The F and E are the complicated parts because they fall outside of the health sector," he explains. "You have to get people from other sectors involved. It's basically trying to convince the wider community that the provision of clean water and better sanitation will have an impact on a disease they probably didn't know existed."

Even with several rounds of MDAs and surgery, Bush says that the disease would come back within a couple of years if hygiene conditions weren't improved.

Danny Haddad, director of the International Trachoma Initiative, an organisation advocating the Safe strategy, says that trachoma stakeholders are trying to leverage the success of the A component to bring on new partners to implement the rest of the strategy. "We're hoping to work with organisations such as Save the Children: they already have hygiene education projects, so when they organise a handwashing day for instance, they could teach people to wash their face too."

The irony with all these interventions is that trachoma would probably disappear of its own accord with better living conditions. It was endemic in much of Europe in the 19th century. The Moorfields Eye Hospital in London was opened in 1805 to tackle the problem. And the disease was deemed such a serious threat in the US that any immigrant suspected of having trachoma was sent on the first boat back to Europe.

But development on this scale will take years in Africa, Asia and Latin America. And in countries such as Ethiopia, Uganda or Sudan, where up to 60% of the population of some districts is infected with trachoma, only the full Safe strategy will yield long-lasting results.

Outside Europe, three countries have already achieved elimination (prevalence of less than 5% for active trachoma, and less than 1 per 1000 for trichiasis): Morocco, Iran and Oman. Ghana and Vietnam are in line to eliminate it within the next two years, and many more are just starting to roll out MDAs, in time hopefully for the 2020 goal.